This invention relates to water-continuous emulsions of silylated elastomeric polymers and processes for preparing such emulsions. In particular, this invention relates to high solids water-continuous emulsions of silylated elastomeric polymers having a solids content greater than 75%, an average particle size less than 5 xcexcm.
Emulsions of high molecular weight polymers are commonly prepared using emulsion polymerization or suspension polymerization techniques. These techniques involve first preparing emulsions or suspensions of the monomer starting materials, and subsequently polymerizing the monomers in-situ to create the high molecular weight polymers. Such techniques avoid the handling and processing problems associated with high molecular weight polymers. However, the type of high molecular weight polymers that can be prepared by such techniques are often limited, and furthermore, the resulting physical properties of the emulsions can often limit their use in many applications.
Alternatively, emulsions of high molecular weight polymers have been prepared by first dispersing the preformed high molecular weight polymer in a solvent. Some representative examples of this art are shown and others further discussed in U.S. Pat. Nos. 4,177,177 and 6,103,786. Also representative of this art are techniques known to create latex emulsions, illustrative examples of this art are taught in U.S. Pat. Nos. 3,360,599, 3,503,917, 4,070,325, 4,243,566, 5,554,726, 5,574,091 and 5,798,410, where the high molecular weight polymer is dispersed in a solvent and is subsequently emulsified.
High internal phase emulsions of high molecular weight polymers are described in U.S. Pat. Nos. 5,539,021, 5,688,842, and 6,156,806. However, these examples also require the use of organic solvents to dissolve the high molecular polymers.
The presence of solvent in emulsions can be hazardous in certain applications or limit usage in other instances because of environmental concerns. For example, many of the commercially important volatile organic solvents are also hazardous to health and environment such as ozone depletion, air pollution, and water contamination. The presence of such volatile solvents in emulsions are highly undesirable to both the producers and the users of emulsions as special handling precautions and equipments are required to minimize the workers"" exposure and release to environment.
Alternative techniques have thus been sought to prepare emulsions of preformed high molecular weight polymers that avoid the shortcomings mentioned above. For example, U.S. Pat. No. 4,123,403 provides a continuous process for preparing aqueous polymer microsuspensions. Aqueous microsuspensions of solid polymers are prepared by a continuous process comprising the steps of (a) forming a heterogeneous composition having a discontinuous aqueous phase and a continuous polymer phase at temperatures above the polymer melting point (e.g. melting above 20xc2x0 C.), and (b) converting the resulting polymer continuous heterogeneous composition to a water-continuous heterogeneous composition. The ""403 patent describes its process as useful for solid polymers, and for thermoplastic solids whose degradation point is somewhat higher than its melting point, and is particularly useful for polymers having a melt flow rate of less than about 40, and temperature sensitive polymers.
Emulsions of high molecular weight polyisobutylene have been reported in Japanese Patent Application Publications 58208341, 59122534, 7173346, 10204234, and 10204235. The publications describe polyisobutylene emulsions having a 1-75% solid content which are prepared with specific types of surfactants, for example a combination of polyoxyethylene-oxypropylene block polymer with polyoxyethylene alkyl ether sulfate ester are described in JP 10204234.
Emulsions of pre-formed high molecular weight silicones have been reported. For example, U.S. Pat. Nos. 5,806,975 and 5,942,574 describe a method for continuous emulsification of organopolysiloxane gums involving a compounding extruder of a specific design, which requires a minimum shear rate of 10 secxe2x88x921. While the ""975 and ""574 patents describe its apparatus and method as capable of emulsifying organopolysiloxane gums having a viscosity in excess of 500,000 centipoise, examples were limited to a trimethylsiloxy-endblocked dimethylpolysiloxane gum with a viscosity of 10 million centipoises (10 KPa-s).
U.S. Pat. No. 5,840,800 describes crosslinked emulsions of pre-formed silicon modified organic polymers having a viscosity of 5-500 Pa-s and a glass transition temperature of less than 20xc2x0 C. The ""800 process describes the formation of a crosslinked emulsion by a) forming an emulsion of silicon modified organic polymers having a viscosity of 5-500 Pa-s (or 0.005-0.5 KPa-s) and b) allowing crosslinking to occur within the emulsion resulting in emulsions of crosslinked polymers.
Processes are needed for the preparation of high solids emulsions of preformed high viscosity elastomeric polymers and elastomeric polymers with curable functionalities. Furthermore, high solids emulsions of elastomeric polymers that are stable with time, and can be further diluted to produce stable emulsions are sought in many industrial processes such as coating applications. A high solids emulsions (e.g. 75% by weight) of such elastomeric polymers will allow development of higher solids, water-based coatings, adhesives, and sealants formulations. The preparation of a high solids emulsion of high viscosity elastomeric polymers with curable functionalities will allow development of curable or crosslinkable coatings, adhesives, and sealants formulations with improved properties, performance and stability over their non-curable or pre-crosslinked elastomeric polymer analogues.
Heretofore a method has not been disclosed for the preparation of stable water-continuous emulsions of high viscosity silylated elastomeric polymers having a high solids content, which also yields stable lower solids emulsions upon dilution.
An object of this invention is to provide a process for preparing water continuous emulsions of silylated elastomeric polymers.
It is a further object of this invention to provide water continuous emulsions of silylated elastomeric polymers with a solids content greater than 75% by weight having a particle size of less than 5 xcexcm that are stable with time.
It is yet a further object of this invention to provide stable emulsions of silylated elastomeric polymers prepared by the dilution of the high solids emulsions of the silylated elastomeric polymer.
This invention relates to a water-continuous emulsion of silylated elastomeric polymers having a solids content of greater than 75%, an average particle size less than 5 xcexcm, and having sufficient stability to produce a stable lower solids emulsion upon dilution with water comprising; a silylated elastomeric polymer, surfactant, water, an optional plasticizer, and an optional low molecular weight acid.
This invention also relates to processes for preparing water-continuous emulsions of silylated elastomeric polymers by; mixing a silylated elastomeric polymer, surfactant, and optionally a plasticizer and a low molecular weight acid, with water to form a water continuous emulsion of the silylated elastomeric polymer having a solids content of greater than 75%, an average particle size less than 5 xcexcm, and having sufficient stability to produce a stable lower solids emulsion upon dilution with water. In a preferred embodiment, the water continuous emulsions of silylated elastomeric polymers can be prepared by mixing a silylated elastomeric polymer, surfactant, optional plasticizer, and optional low molecular weight acid with incremental portions of water, whereby each incremental portion comprises less than 8 weight % of the premix and each incremental portion of water is added successively to the previous after the dispersion of the previous incremental portion of water, wherein sufficient incremental portions of water are added to form the water-continuous emulsion of the silylated elastomeric polymer. The present inventors have unexpectedly found this stepwise addition of water in small incremental portions allows for the formation of the emulsion and enhances the emulsion stability at relatively high solids contents.